Critical to the development of the nervous system is a series of events that depend upon cell recognition processes. These include the regulation of cell proliferation and differentiation, neuron migration, axonal outgrowth, and ultimately target cell recognition. The long-term goal of my laboratory has been to identify novel neural proteins that are expressed at these critical stages of neural development, and thus are likely to play an integral role in these cell recognition processes. Using monoclonal antibodies (MAbs) my laboratory has identified two novel neural proteins in the embryonic chick nervous system, which are associated with putative barrier structures in the CNS. Barrier structures have recently received increasing attention, since they may regulate axonal growth by inhibitory mechanisms. The two proteins identified in my laboratory are developmentally down-regulated during CNS development, and are not expressed in adult brain. The first protein, named Embryonal Avian Polypeptide of 300 kDa (EAP-300), has been shown to be restricted to dorsal midline structures in embryonic chick CNS, the glial knot barrier of the diencephalon, and is also expressed by radial glia in the developing cerebellum. The second molecule, a keratan sulfate proteoglycan (KSPG), was initially identified by its co-purification with EAP-300 under non-dissociating conditions. Antibodies to this KSPG stain the dorsal midline region of the chick CNS, suggesting that the association between these two molecules may have functional implications. It has been shown that the purified KSPG, named claustrin (from the Latin,claustra= barrier), inhibits cell adhesion on laminin or NCAM substrata. The studies proposed here will focus on a characterization of these two novel proteins, with an emphasis on their molecular and functional properties. The specific aims of this proposal are:1) to characterize these barrier-associated molecules, with an emphasis on their immunohistochemical distribution during development, an analysis of the possible functional interaction between claustrin and EAP-300, and the biochemical properties of the molecules; 2) to examine the function of EAP-300 and claustrin, and determine their role in the function of CNS barriers in situ; and 3) to isolate cDNAs coding for EAP-300 and claustrin, with an emphasis on the characterization of the developmental expression of EAP-300 and claustrin mRNA.